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wonderful Universal voltage inputs ?

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suncq

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I find a industrial product that Universal voltage inputs are polarity independent. Connect to any range voltage in your control
panel - from +/- 12 VAC/VDC to 120 VAC/VDC. Does anybody know how to realize this wonderful function?
thanks in advance!
suncq@126.com
 

Polarity independent is easy?

But i havnt seen such a wide voltage input? what is it?
do you know the working voltage of the board?

Nandhu
 

thanks for your reply.It use Photocoupler so it doesn't matter with working voltage of the board.
 

Hi,
For polarity you use a diode bridge and for opto driving use a 5mA constant current source after the bridge around a transistr like MJE 340, you can realise a universal input as specified by you. Even though it is costly, it provides a foolproof solution in an industrial environment.
Regards,
Laktronics
 

Depending on speed and noise immunity requirements, also much lower optocoupler drive currents can be used. I sometimes designed such circuits with passive parts input only.
 

thanks Laktronics and FvM. Could you post the circuit?
 

Hi,
Try this circuit. I still feel a better option with a switching regulator IC may be possible to reduce the wasted power.
Regards,
Laktronics
 

thanks for Laktronics!but I have some questions for you. why does R2(10k) need 5W?if I put the 220VAc in input, which element do I need to change?
 

Hi,
Good that you have asked this question, by the way there is a mistake in the circuit, the rectifier diode should be 4x1N4003 or higher numbers of 4000 series to be able to handle 120 V AC peaks. I will see if I can reload the schematic with this correction.
Sorry for that. Now regarding the requirement of 10k,5W, you can see that when 120VAC is rectified, you get a peak voltage of about 170V (120*√2). Most of this voltage gets dropped across the collector base of the transistor and its parallel 10K resistor, which means, it has to handle a power of 170*170/10k, typically around 2.5W Watts. Even in this case, we have not considered the allowed variation of 15% on the commercial 120V supply.

Now regarding usage of 220V AC, you can find what all will have to change, with a rectified peak of 300V, you will need to use only 1N4004 and above as rectifiers, the tansistor should be changed for higher VCEO and the wattage of 10k to about 20W?
The real problem is in the range of input voltage, since the system has to work down to 12V DC. And all these, only to supply a load of around 10mW (5mA*2V), of opto power,what a colosal waste of power; the 'Greens' will have sufficient reason to revolt ! That is why I lamented in the previous post about my inability to locate a suitable switcher with such wide ranging inputs to supply this trivial load and to save the power.
Regards,
Laktronics
 

many thanks for Laktronics such detail description.I will put this kind of input circuit to work in my next product design.
 

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